A vacuum valve has its insulating performance ensured in such a way that the outer peripheral surface of a vacuum vessel having a movable electrode and a stationary electrode inside is molded with a resin, for example, an epoxy resin being an outer peripheral insulator (hereinbelow, termed “resin molding”).
In general, it is practiced to apply thermal stress relaxation members to only required parts, i.e., parts requiring thermal stress relaxation, not to all the outer peripheral surface of a vacuum vessel 1A (refer to, for example, Patent Document 1). Signs 3B in FIG. 8 of Patent Document 1 denote room-temperature vulcanizing type silicone rubber [hereinbelow, termed “RTV (Room Temperature Vulcanizable) rubber”] being the stress relaxation members which are applied as coatings so as to respectively cover thermal stress concentration parts 2C being the thermal stress relaxation-requiring parts of the outer peripheral surface of the vacuum vessel 1A. Incidentally, there are disposed metal-made flanges 2a which block up both the ends of a vacuum vessel 2, and a ceramics-made insulating tube 2b which forms the body portion of the vacuum vessel 2.
The RTV rubber or the like is a liquefied and viscous rubber, which is applied as the coatings to the thermal stress concentration parts 2c surrounding the outer peripheral surface of the vacuum vessel 2, to appropriate thicknesses, and is then vulcanized. Since the coating operation needs to be performed with scrupulous care so as not to involve air bubbles causing partial discharges, into the RTV rubber, much labor and a long time have been expended on the execution of the thermal stress relaxation members.
Besides, the RTV rubber differs in thermal expansion coefficient from the epoxy resin or the like which insulates the outer peripheral surface of the vacuum vessel. It is therefore apprehended that, when the vacuum vessel becomes a normal temperature of about 20° C. after having been molded at a high temperature exceeding 100° C., gaps will appear between the RTV rubber and the epoxy resin, to form causes for partial discharges.
Patent Document 1: JP-A-2002-358861 (FIG. 8)